Methods and systems for establishing retrograde carotid arterial blood flow

ABSTRACT

Interventional procedures on the carotid arteries are performed through a transcervical access while retrograde blood flow is established from the internal carotid artery to a venous or external location. A system for use in accessing and treating a carotid artery includes an arterial access device, a shunt fluidly connected to the arterial access device, and a flow control assembly coupled to the shunt and adapted to regulate blood flow through the shunt between at least a first blood flow state and at least a second blood flow state. The flow control assembly includes one or more components that interact with the blood flow through the shunt.

REFERENCE TO PRIORITY DOCUMENT

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/176,250, entitled “Methods and Systems for EstablishingRetrograde Carotid Arterial Blood Flow”, filed on Jul. 18, 2008, whichclaims the benefit under 35 U.S.C. §119(e) of the following U.S.Provisional Patent Applications: (1) U.S. Provisional Patent ApplicationSer. No. 60/950,384 filed on Jul. 18, 2007 and (2) U.S. ProvisionalPatent Application Ser. No. 61/026,308 filed on Feb. 5, 2008. Priorityof the aforementioned filing dates is hereby claimed, and thedisclosures of the patent applications are hereby incorporated byreference in their entirety.

BACKGROUND

The present disclosure relates generally to medical methods and devices.More particularly, the present disclosure relates to methods and systemsfor accessing the carotid arterial vasculature and establishingretrograde blood flow during performance of carotid artery stenting andother procedures.

Carotid artery disease usually consists of deposits of plaque P whichnarrow the junction between the common carotid artery CCA and theinternal carotid artery ICA, an artery which provides blood flow to thebrain (FIG. 5). These deposits increase the risk of embolic particlesbeing generated and entering the cerebral vasculature, leading toneurologic consequences such as transient ischemic attacks TIA, ischemicstroke, or death. In addition, should such narrowings become severe,blood flow to the brain is inhibited with serious and sometimes fatalconsequences.

Two principal therapies are employed for treating carotid arterydisease. The first is carotid endarterectomy CEA, an open surgicalprocedure which relies on occluding the common, internal and externalcarotid arteries, opening the carotid artery at the site of the disease(usually the carotid bifurcation where the common carotid artery CCAdivides into the internal carotid artery ICA and external carotid arteryECA), dissecting away and removing the plaque P, and then closing thecarotid artery. The second procedure relies on stenting of the carotidarteries, referred to as carotid artery stenting CAS, typically at oracross the branch from the common carotid artery CAA into the internalcarotid artery ICA, or entirely in the internal carotid artery. Usually,a self-expanding stent is introduced through percutaneous puncture intothe femoral artery in the groin and up the aortic arch into the targetcommon carotid artery CCA.

In both these approaches, the patient is at risk of emboli beingreleased into the cerebral vasculature via the internal carotid arteryICA. The clinical consequence of emboli release into the externalcarotid artery ECA, an artery which provides blood to facial structures,is less significant. During CEA, the risk of emboli release into theinternal carotid artery ICA is minimized by debriding and vigorouslyflushing the arteries before closing the vessels and restoring bloodflow. During the procedure while the artery is opened, all the carotidarteries are occluded so particles are unable to enter the vasculature.

In carotid stenting CAS procedures, adjunct embolic protection devicesare usually used to at least partially alleviate the risk of emboli. Anexample of these devices are distal filters, which are deployed in theinternal carotid artery distal to the region of stenting. The filter isintended to capture the embolic particles to prevent passage into thecerebral vasculature. Such filtering devices, however, carry certainlimitations. They must be advanced to the target vessel and cross thestenosis prior to deployment, which exposes the cerebral vascular toembolic showers; they are not always easy to advance, deploy, and removethrough a tight stenosis and/or a severely angulated vasculature; andfinally, they only filter particles larger than the filter pore size,typically 100 to 120 μm. Also, these devices do not filter 100% of theflow due to incomplete wall opposition of the filter, and furthermorethere is a risk of debris escape during filter retrieval.

Of particular interest to the present disclosure, an alternative methodfor reducing the risk of emboli release into the internal carotid arteryICA has been proposed for use during carotid stenting CAS proceduresutilizing the concept of reversing the flow in the internal carotidartery ICA to prevent embolic debris entering the cerebral vasculature.Although a number of specific protocols have been described, theygenerally rely on placing a sheath via the femoral artery (transfemoralaccess) into the common carotid artery. Flow in the common carotidartery is occluded, typically by inflating a balloon on the distal tipof the sheath. Flow into the external carotid artery ECA may also beoccluded, typically using a balloon catheter or balloon guidewireintroduced through the sheath. The sheath is then connected to a venouslocation or to a low pressure external receptacle in order to establisha reverse or retrograde flow from the internal carotid artery throughthe sheath and away from the cerebral vasculature. After such reverse orretrograde flow is established, the stenting procedure may be performedwith a greatly reduced risk of emboli entering the cerebral vasculature.

An alternate system which simply halts forward flow in the ICA consistsof a carotid access sheath with two integral balloons: an ECA occlusionballoon at the distal tip, and a CCA occlusion balloon placed some fixeddistance proximal to the ECA balloon. Between the two balloons is anopening for delivery of the interventional carotid stenting devices.This system does not reverse flow from the ICA to the venous system, butinstead relies on blocking flow and performing aspiration to removeembolic debris prior to establishing forward flow in the ICA.

While such reverse or static flow protocols for performing stenting andother interventional procedures in the carotid vasculature hold greatpromise, such methods have generally required the manipulation ofmultiple separate access and occlusion components. Moreover, theprotocols have been rather complicated, requiring many separate steps,limiting their performance to only the most skilled vascular surgeons,interventional radiologists and cardiologists. In addition, due to thesize limitations of the femoral access, the access devices themselvesprovide a very high resistance to flow, limiting the amount of reverseflow and/or aspiration possible. Furthermore, the requirement to occludethe external carotid artery adds risk and complexity to the procedure.The balloon catheter for occluding the external carotid artery canbecome trapped in the arterial wall in cases where the stent is placedacross the bifurcation from the common carotid artery to the internalcarotid artery, and may cause damage to the deployed stent when it isremoved.

None of the cerebral protection devices and methods described offerprotection after the procedure. However, generation of embolic particleshave been measured up to 48 hours or later, after the stent procedure.During CEA, flushing at the end of the procedure while blocking flow tothe internal carotid artery ICA may help reduce post-procedure emboligeneration. A similar flushing step during CAS may also reduce embolirisk. Additionally, a stent which is designed to improve entrapment ofembolic particles may also reduce post-procedure emboli.

In addition, all currently available carotid stenting and cerebralprotection systems are designed for access from the femoral artery.Unfortunately, the pathway from the femoral artery to the common carotidartery is relatively long, has several turns which in some patients canbe quite angulated, and often contains plaque and other diseases. Theportion of the procedure involving access to the common carotid arteryfrom the femoral artery can be difficult and time consuming as well asrisk generating showers of embolic debris up both the target and theopposite common carotid artery and thence to the cerebral vasculature.Some studies suggest that up to half, or more, of embolic complicationsduring CAS procedures occur during access to the CCA. None of theprotocols or systems offer protection during this portion of theprocedure.

Recently, a reverse flow protocol having an alternative access route tothe carotid arteries has been proposed by Criado. This alternative routeconsists of direct surgical access to the common carotid artery CCA,called transcervical access. Transcervical access greatly shortens thelength and tortuosity of the pathway from the vascular access point tothe target treatment site thereby easing the time and difficulty of theprocedure. Additionally, this access route reduces the risk of emboligeneration from navigation of diseased, angulated, or tortuous aorticarch or common carotid artery anatomy.

The Criado protocol is described in several publications in the medicalliterature cited below. As shown in FIG. 3, the Criado protocol uses aflow shunt which includes an arterial sheath 210 and a venous sheath212. Each sheath has a side arm 214, terminating in a stopcock 216. Thetwo sheaths stopcocks are connected by a connector tubing 218, thuscompleting a reverse flow shunt from the arterial sheath 210 to thevenous sheath 212 The arterial sheath is placed in the common carotidartery CCA through an open surgical incision in the neck below thecarotid bifurcation. Occlusion of the common carotid artery CCA isaccomplished using a temporary vessel ligation, for example using aRummel tourniquet and umbilical tape or vessel loop. The venous returnsheath 212 is placed in the internal jugular vein IJV (FIG. 3), also viaan open surgical incision. Retrograde flow from the internal carotidartery ICA and the external carotid artery ECA may then be establishedby opening the stopcock 216. The Criado protocol is an improvement overthe earlier retrograde flow protocols since it eliminates the need forfemoral access. Thus, the potential complications associated with thefemoral access are completely avoided. Furthermore, the lower flowrestrictions presented by the shorter access route offer the opportunityfor more vigorous reverse flow rate, increasing the efficiency ofembolic debris removal. Because of these reduced flow restrictions, thedesired retrograde flow of the internal carotid artery ICA may beestablished without occluding the external carotid artery ECA, asrequired by the earlier protocols.

While a significant improvement over the femoral access-based retrogradeflow protocols, the Criado protocol and flow shunt could still benefitfrom improvement. In particular, the existing arterial and venoussheaths used in the procedure still have significant flow restrictionsin the side arms 214 and stopcocks 216. When an interventional catheteris inserted into the arterial access sheath, the reverse flow circuitresistance is at a maximum. In some percentage of patients, the externalcarotid artery ECA perfusion pressure is greater than the internalcarotid artery ICA perfusion pressure. In these patients, thisdifferential pressure might drive antegrade flow into the ICA from theECA. A reverse flow shunt with lower flow resistance could guaranteereversal of flow in both the ECA and ICA despite a pressure gradientfrom the ECA to the ICA.

In addition, there is no means to monitor or regulate the reverse flowrate. The ability to increase and/or modulate the flow rate would givethe user the ability to set the reverse flow rate optimally to thetolerance and physiology of the patient and the stage of the procedure,and thus offer improved protection from embolic debris. Further, thesystem as described by Criado relies on manually turning one or morestopcocks to open and close the reverse flow shunt, for example duringinjection of contrast medium to facilitate placement of the CAS systems.Finally, the Criado protocol relies on open surgical occlusion of thecommon carotid artery, via a vessel loop or Rummel tourniquet. A systemwith means to occlude the common carotid artery intravascularly, forexample with an occlusion element on the arterial access sheath, wouldallow the entire procedure to be performed using percutaneoustechniques. A percutaneous approach would limit the size and associatedcomplications of a surgical incision, as well as enable non-surgicalphysicians to perform the procedure.

For these reasons, it would be desirable to provide improved methods,apparatus, and systems for performing transcervical access, retrogradeflow and flushing procedures and implantation of a carotid stent in thecarotid arterial vasculature to reduce the risk of procedural andpost-procedural emboli, to improve the level of hemostasis throughoutthe procedure, and to improve the ease and speed of carotid arterystenting. The methods, apparatus, and system should simplify theprocedure to be performed by the physician as well as reduce the risk ofimproperly performing the procedures and/or achieving insufficientretrograde flow and flushing to protect against emboli release. Thesystems should provide individual devices and components which arereadily used with each other and which protect against emboli-relatedcomplications. The methods and systems should also provide forconvenient and preferably automatic closure of any and all arterialpenetrations at the end of the procedure to prevent unintended bloodloss. Additionally, the systems, apparatus, and methods should besuitable for performance by either open surgical or percutaneous accessroutes into the vasculature. Additionally, the methods, apparatus, andsystems should enable implantation of an intravascular prostheticimplant which lowers post procedural complications. At least some ofthese objectives will be met by the inventions described herein below.

SUMMARY

The disclosed methods, apparatus, and systems establish and facilitateretrograde or reverse flow blood circulation in the region of thecarotid artery bifurcation in order to limit or prevent the release ofemboli into the cerebral vasculature, particularly into the internalcarotid artery. The methods are particularly useful for interventionalprocedures, such as stenting and angioplasty, atherectomy, performedthrough a transcervical approach or transfemoral into the common carotidartery, either using an open surgical technique or using a percutaneoustechnique, such as a modified Seldinger technique.

Access into the common carotid artery is established by placing a sheathor other tubular access cannula into a lumen of the artery, typicallyhaving a distal end of the sheath positioned proximal to the junction orbifurcation B (FIG. 5) from the common carotid artery to the internaland external carotid arteries. The sheath may have an occlusion memberat the distal end, for example a compliant occlusion balloon. A catheteror guidewire with an occlusion member, such as a balloon, may be placedthrough the access sheath and positioned in the proximal externalcarotid artery ECA to inhibit the entry of emboli, but occlusion of theexternal carotid artery is usually not necessary. A second return sheathis placed in the venous system, for example the internal jugular veinIJV or femoral vein FV. The arterial access and venous return sheathsare connected to create an external arterial-venous shunt.

Retrograde flow is established and modulated to meet the patient'srequirements. Flow through the common carotid artery is occluded, eitherwith an external vessel loop or tape, a vascular clamp, an internalocclusion member such as a balloon, or other type of occlusion means.When flow through the common carotid artery is blocked, the naturalpressure gradient between the internal carotid artery and the venoussystem will cause blood to flow in a retrograde or reverse directionfrom the cerebral vasculature through the internal carotid artery andthrough the shunt into the venous system.

Alternately, the venous sheath could be eliminated and the arterialsheath could be connected to an external collection reservoir orreceptacle. The reverse flow could be collected in this receptacle. Ifdesired, the collected blood could be filtered and subsequently returnedto the patient during or at the end of the procedure. The pressure ofthe receptacle could be open to zero pressure, causing the pressuregradient to create blood to flow in a reverse direction from thecerebral vasculature to the receptacle or the pressure of the receptaclecould be a negative pressure.

Optionally, to achieve or enhance reverse flow from the internal carotidartery, flow from the external carotid artery may be blocked, typicallyby deploying a balloon or other occlusion element in the externalcarotid just above (i.e., distal) the bifurcation within the internalcarotid artery.

Although the procedures and protocols described hereinafter will beparticularly directed at carotid stenting, it will be appreciated thatthe methods for accessing the carotid artery described herein would alsobe useful for angioplasty, artherectomy, and any other interventionalprocedures which might be carried out in the carotid arterial system,particularly at a location near the bifurcation between the internal andexternal carotid arteries. In addition, it will be appreciated that someof these access, vascular closure, and embolic protection methods willbe applicable in other vascular interventional procedures, for examplethe treatment of acute stroke.

The present disclosure includes a number of specific aspects forimproving the performance of carotid artery access protocols. At leastmost of these individual aspects and improvements can be performedindividually or in combination with one or more other of theimprovements in order to facilitate and enhance the performance of theparticular interventions in the carotid arterial system.

In one aspect, there is disclosed a system for use in accessing andtreating a carotid artery, said system. The system comprises an arterialaccess device adapted to be introduced into a common carotid artery andreceive blood flow from the common carotid artery; a shunt fluidlyconnected to the arterial access device, wherein the shunt provides apathway for blood to flow from the arterial access device to a returnsite; and a flow control assembly coupled to the shunt and adapted toregulate blood flow through the shunt between at least a first bloodflow state and at least a second blood flow state, wherein the flowcontrol assembly includes one or more components that interact with theblood flow through the shunt.

In another aspect, there is disclosed a system for use in accessing andtreating a carotid artery. The system comprises an arterial accessdevice adapted to be introduced into a common carotid artery and receiveblood flow from the common carotid artery; a shunt fluidly connected tothe arterial access device, wherein the shunt provides a pathway forblood to flow from the arterial access device to a return site; a flowmechanism coupled to the shunt and adapted to vary the blood flowthrough the shunt between a first blood flow rate and a second bloodflow rate; and a controller that automatically interacts with the flowmechanism to regulate blood flow through the shunt between the firstblood flow rate and the second blood flow rate without requiring inputfrom a user.

In another aspect, there is disclosed a device for use in accessing andtreating a carotid artery. The device comprises a distal sheath having adistal end adapted to be introduced into the common carotid artery, aproximal end, and a lumen extending between the distal and proximalends; a proximal extension having a distal end, a proximal end, and alumen therebetween, wherein the distal end of the proximal extension isconnected to the proximal end of the sheath at a junction so that thelumens of each are contiguous; a flow line having a lumen, said flowline connected near the junction so that blood flowing into the distalend of the sheath can flow into the lumen of the flow line; and ahemostasis valve at the proximal end of the proximal extension, saidhemostasis valve being adapted to inhibit blood flow from the proximalextension while allowing catheter introduction through the proximalextension and into the distal sheath.

In another aspect, there is disclosed a method for accessing andtreating a carotid artery. The method comprises forming a penetration ina wall of a common carotid artery; positioning an access sheath throughthe penetration; blocking blood flow from the common carotid artery pastthe sheath; allowing retrograde blood flow from the carotid artery intothe sheath and from the sheath via a flow path to a return site; andmodifying blood flow through the flow path based on feedback data.

In another aspect, there is disclosed a method for accessing andtreating a carotid artery. The method comprises forming a penetration ina wall of a common carotid artery; positioning an access sheath throughthe penetration; blocking blood flow from the common carotid artery pastthe sheath; allowing retrograde blood flow from the carotid artery intothe sheath and from the sheath via a flow path to a return site; andmonitoring flow through the flow path.

In another aspect, there is disclosed a method for accessing andtreating a carotid artery. The method comprises: forming a penetrationin a wall of a common carotid artery; positioning an arterial accesssheath through the penetration; blocking blood flow from the commoncarotid artery past the sheath; allowing retrograde blood flow from theinternal carotid artery into the sheath while the common carotid arteryremains blocked; and adjusting the state of retrograde blood flowthrough the sheath.

In another aspect, there is disclosed a method for accessing andtreating a carotid artery. The method comprises forming a penetration ina wall of a common carotid artery; positioning an arterial access sheaththrough the penetration; blocking blood flow from the common carotidartery past the sheath; allowing retrograde blood flow from the internalcarotid artery into the sheath while the common carotid artery remainsblocked; and adjusting a rate of retrograde blood flow from the sheathto as high a level as the patient will tolerate, wherein said adjustedrate is a baseline.

Other features and advantages should be apparent from the followingdescription of various embodiments, which illustrate, by way of example,the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of a retrograde blood flow systemincluding a flow control assembly wherein an arterial access deviceaccesses the common carotid artery via a transcervical approach and avenous return device communicates with the internal jugular vein.

FIG. 1B is a schematic illustration of a retrograde blood flow systemwherein an arterial access device accesses the common carotid artery viaa transcervical approach and a venous return device communicates withthe femoral vein.

FIG. 1C is a schematic illustration of a retrograde blood flow systemwherein an arterial access device accesses the common carotid artery viaa transfemoral approach and a venous return device communicates with thefemoral vein.

FIG. 1D is a schematic illustration of a retrograde blood flow systemwherein retrograde flow is collected in an external receptacle.

FIG. 2A is an enlarged view of the carotid artery wherein the carotidartery is occluded and connected to a reverse flow shunt, and aninterventional device, such as a stent delivery system or other workingcatheter, is introduced into the carotid artery via an arterial accessdevice.

FIG. 2B is an alternate system wherein the carotid artery is connectedto a reverse flow shunt and an interventional device, such as a stentdelivery system or other working catheter, is introduced into thecarotid artery via an arterial access device, and the carotid artery isoccluded with a separate occlusion device.

FIG. 2C is an alternate system wherein the carotid artery is occludedand the artery is connected to a reverse flow shunt via an arterialaccess device and the interventional device, such as a stent deliverysystem, is introduced into the carotid artery via an arterial introducerdevice.

FIG. 3 illustrates a prior art Criado flow shunt system.

FIG. 4 illustrates a normal cerebral circulation diagram including theCircle of Willis.

FIG. 5 illustrates the vasculature in a patient's neck, including thecommon carotid artery CCA, the internal carotid artery ICA, the externalcarotid artery ECA, and the internal jugular vein IJV.

FIG. 6A illustrates an arterial access device useful in the methods andsystems of the present disclosure.

FIG. 6B illustrates an additional arterial access device constructionwith a reduced diameter distal end.

FIGS. 7A and 7B illustrate a tube useful with the sheath of FIG. 6A.

FIG. 8A illustrates an additional arterial access device constructionwith an expandable occlusion element.

FIG. 8B illustrates an additional arterial access device constructionwith an expandable occlusion element and a reduced diameter distal end.

FIG. 9 illustrates a first embodiment of a venous return device usefulin the methods and systems of the present disclosure.

FIG. 10 illustrates an alternative venous return device useful in themethods and systems of the present disclosure.

FIG. 11 illustrates the system of FIG. 1 including a flow controlassembly.

FIG. 12A-12D, FIGS. 13A-13D, FIGS. 14A and 14B, FIGS. 15A-15D, and FIGS.16A and 16B, illustrate different embodiments of a variable flowresistance component useful in the methods and systems of the presentdisclosure.

FIGS. 17A-17B, FIGS. 18A-18B, FIGS. 19A-19D, and FIGS. 20A-20Billustrate further embodiments of a variable flow resistance systemuseful in the methods and systems of the present disclosure.

FIGS. 21A-21E illustrate the exemplary blood flow paths during aprocedure for implanting a stent at the carotid bifurcation inaccordance with the principles of the present disclosure.

DETAILED DESCRIPTION

FIG. 1A shows a first embodiment of a retrograde flow system 100 that isadapted to establish and facilitate retrograde or reverse flow bloodcirculation in the region of the carotid artery bifurcation in order tolimit or prevent the release of emboli into the cerebral vasculature,particularly into the internal carotid artery. The system 100 interactswith the carotid artery to provide retrograde flow from the carotidartery to a venous return site, such as the internal jugular vein (or toanother return site such as another large vein or an external receptaclein alternate embodiments.) The retrograde flow system 100 includes anarterial access device 110, a venous return device 115, and a shunt 120that provides a passageway for retrograde flow from the arterial accessdevice 110 to the venous return device 115. A flow control assembly 125interacts with the shunt 120. The flow control assembly 125 is adaptedto regulate and/or monitor the retrograde flow from the common carotidartery to the internal jugular vein, as described in more detail below.The flow control assembly 125 interacts with the flow pathway throughthe shunt 120, either external to the flow path, inside the flow path,or both. The arterial access device 110 at least partially inserts intothe common carotid artery CCA and the venous return device 115 at leastpartially inserts into a venous return site such as the internal jugularvein IJV, as described in more detail below. The arterial access device110 and the venous return device 115 couple to the shunt 120 atconnection locations 127 a and 127 b. When flow through the commoncarotid artery is blocked, the natural pressure gradient between theinternal carotid artery and the venous system causes blood to flow in aretrograde or reverse direction RG (FIG. 2A) from the cerebralvasculature through the internal carotid artery and through the shunt120 into the venous system. The flow control assembly 125 modulates,augments, assists, monitors, and/or otherwise regulates the retrogradeblood flow.

In the embodiment of FIG. 1A, the arterial access device 110 accessesthe common carotid artery CCA via a transcervical approach.Transcervical access provides a short length and non-tortuous pathwayfrom the vascular access point to the target treatment site therebyeasing the time and difficulty of the procedure, compared for example toa transfemoral approach. Additionally, this access route reduces therisk of emboli generation from navigation of diseased, angulated, ortortuous aortic arch or common carotid artery anatomy. At least aportion of the venous return device 115 is placed in the internaljugular vein IJV. In an embodiment, transcervical access to the commoncarotid artery is achieved percutaneously via an incision or puncture inthe skin through which the arterial access device 110 is inserted. If anincision is used, then the incision can be about 0.5 cm in length. Anocclusion element 129, such as an expandable balloon, can be used toocclude the common carotid artery CCA at a location proximal of thedistal end of the arterial access device 110. The occlusion element 129can be located on the arterial access device 110 or it can be located ona separate device. In an alternate embodiment, the arterial accessdevice 110 accesses the common carotid artery CCA via a direct surgicaltranscervical approach. In the surgical approach, the common carotidartery can be occluded using a tourniquet 2105. The tourniquet 2105 isshown in phantom to indicate that it is a device that is used in theoptional surgical approach.

In another embodiment, shown in FIG. 1B, the arterial access device 110accesses the common carotid artery CCA via a transcervical approachwhile the venous return device 115 access a venous return site otherthan the jugular vein, such as a venous return site comprised of thefemoral vein FV. The venous return device 115 can be inserted into acentral vein such as the femoral vein FV via a percutaneous puncture inthe groin.

In another embodiment, shown in FIG. 1C, the arterial access device 110accesses the common carotid artery via a femoral approach. According tothe femoral approach, the arterial access device 110 approaches the CCAvia a percutaneous puncture into the femoral artery FA, such as in thegroin, and up the aortic arch AA into the target common carotid arteryCCA. The venous return device 115 can communicate with the jugular veinJV or the femoral vein FV.

FIG. 1D shows yet another embodiment, wherein the system providesretrograde flow from the carotid artery to an external receptacle 130rather than to a venous return site. The arterial access device 110connects to the receptacle 130 via the shunt 120, which communicateswith the flow control assembly 125. The retrograde flow of blood iscollected in the receptacle 130. If desired, the blood could be filteredand subsequently returned to the patient. The pressure of the receptacle130 could be set at zero pressure (atmospheric pressure) or even lower,causing the blood to flow in a reverse direction from the cerebralvasculature to the receptacle 130. Optionally, to achieve or enhancereverse flow from the internal carotid artery, flow from the externalcarotid artery can be blocked, typically by deploying a balloon or otherocclusion element in the external carotid artery just above thebifurcation with the internal carotid artery. FIG. 1D shows the arterialaccess device 110 arranged in a transcervical approach with the CCAalthough it should be appreciated that the use of the externalreceptacle 130 can also be used with the arterial access device 110 in atransfemoral approach.

With reference to the enlarged view of the carotid artery in FIG. 2A, aninterventional device, such as a stent delivery system 135 or otherworking catheter, can be introduced into the carotid artery via thearterial access device 110, as described in detail below. The stentdelivery system 135 can be used to treat the plaque P such as to deploya stent into the carotid artery. The arrow RG in FIG. 2A represents thedirection of retrograde flow.

FIG. 2B shows another embodiment, wherein the arterial access device 110is used for the purpose of creating an arterial-to-venous shunt as wellas introduction of at least one interventional device into the carotidartery. A separate arterial occlusion device 112 with an occlusionelement 129 can be used to occlude the common carotid artery CCA at alocation proximal to the distal end of the arterial access device 110.

FIG. 2C shows yet another embodiment wherein the arterial access device110 is used for the purpose of creating an arterial-to-venous shunt aswell as arterial occlusion using an occlusion element 129. A separatearterial introducer device can be used for the introduction of at leastone interventional device into the carotid artery at a location distalto the arterial access device 110.

DESCRIPTION OF ANATOMY Collateral Brain Circulation

The Circle of Willis CW is the main arterial anastomatic trunk of thebrain where all major arteries which supply the brain, namely the twointernal carotid arteries (ICAs) and the vertebral basilar system,connect. The blood is carried from the Circle of Willis by the anterior,middle and posterior cerebral arteries to the brain. This communicationbetween arteries makes collateral circulation through the brainpossible. Blood flow through alternate routes is made possible therebyproviding a safety mechanism in case of blockage to one or more vesselsproviding blood to the brain. The brain can continue receiving adequateblood supply in most instances even when there is a blockage somewherein the arterial system (e.g., when the ICA is ligated as describedherein). Flow through the Circle of Willis ensures adequate cerebralblood flow by numerous pathways that redistribute blood to the deprivedside.

The collateral potential of the Circle of Willis is believed to bedependent on the presence and size of its component vessels. It shouldbe appreciated that considerable anatomic variation between individualscan exist in these vessels and that many of the involved vessels may bediseased. For example, some people lack one of the communicatingarteries. If a blockage develops in such people, collateral circulationis compromised resulting in an ischemic event and potentially braindamage. In addition, an autoregulatory response to decreased perfusionpressure can include enlargement of the collateral arteries, such as thecommunicating arteries, in the Circle of Willis. An adjustment time isoccasionally required for this compensation mechanism before collateralcirculation can reach a level that supports normal function. Thisautoregulatory response can occur over the space of 15 to 30 seconds andcan only compensate within a certain range of pressure and flow drop.Thus, it is possible for a transient ischemic attack to occur during theadjustment period. Very high retrograde flow rate for an extended periodof time can lead to conditions where the patient's brain is not gettingenough blood flow, leading to patient intolerance as exhibited byneurologic symptoms or in some cases a transient ischemic attack.

FIG. 4 depicts a normal cerebral circulation and formation of Circle ofWillis CW. The aorta AO gives rise to the brachiocephalic artery BCA,which branches into the left common carotid artery LCCA and leftsubclavian artery LSCA. The aorta AO further gives rise to the rightcommon carotid artery RCCA and right subclavian artery RSCA. The leftand right common carotid arteries CCA gives rise to internal carotidarteries ICA which branch into the middle cerebral arteries MCA,posterior communicating artery PcoA, and anterior cerebral artery ACA.The anterior cerebral arteries ACA deliver blood to some parts of thefrontal lobe and the corpus striatum. The middle cerebral arteries MCAare large arteries that have tree-like branches that bring blood to theentire lateral aspect of each hemisphere of the brain. The left andright posterior cerebral arteries PCA arise from the basilar artery BAand deliver blood to the posterior portion of the brain (the occipitallobe).

Anteriorly, the Circle of Willis is formed by the anterior cerebralarteries ACA and the anterior communicating artery ACoA which connectsthe two ACAs. The two posterior communicating arteries PCoA connect theCircle of Willis to the two posterior cerebral arteries PCA, whichbranch from the basilar artery BA and complete the Circle posteriorly.

The common carotid artery CCA also gives rise to external carotid arteryECA, which branches extensively to supply most of the structures of thehead except the brain and the contents of the orbit. The ECA also helpssupply structures in the neck and face.

Carotid Artery Bifurcation

FIG. 5 shows an enlarged view of the relevant vasculature in thepatient's neck. The common carotid artery CCA branches at bifurcation Binto the internal carotid artery ICA and the external carotid arteryECA. The bifurcation is located at approximately the level of the fourthcervical vertebra. FIG. 5 shows plaque P formed at the bifurcation B.

As discussed above, the arterial access device 110 can access the commoncarotid artery CCA via a transcervical approach. Pursuant to thetranscervical approach, the arterial access device 110 is inserted intothe common carotid artery CCA at an arterial access location L, whichcan be, for example, a surgical incision or puncture in the wall of thecommon carotid artery CCA. There is typically a distance D of around 5to 7 cm between the arterial access location L and the bifurcation B.When the arterial access device 110 is inserted into the common carotidartery CCA, it is undesirable for the distal tip of the arterial accessdevice 110 to contact the bifurcation B as this could disrupt the plaqueP and cause generation of embolic particles. In order to minimize thelikelihood of the arterial access device 110 contacting the bifurcationB, in an embodiment only about 2-4 cm of the distal region of thearterial access device is inserted into the common carotid artery CCAduring a procedure.

The common carotid arteries are encased on each side in a layer offascia called the carotid sheath. This sheath also envelops the internaljugular vein and the vagus nerve. Anterior to the sheath is thesternocleidomastoid muscle. Transcervical access to the common carotidartery and internal jugular vein, either percutaneous or surgical, canbe made immediately superior to the clavicle, between the two heads ofthe sternocleidomastoid muscle and through the carotid sheath, with caretaken to avoid the vagus nerve.

At the upper end of this sheath, the common carotid artery bifurcatesinto the internal and external carotid arteries. The internal carotidartery continues upward without branching until it enters the skull tosupply blood to the retina and brain. The external carotid arterybranches to supply blood to the scalp, facial, ocular, and othersuperficial structures. Intertwined both anterior and posterior to thearteries are several facial and cranial nerves. Additional neck musclesmay also overlay the bifurcation. These nerve and muscle structures canbe dissected and pushed aside to access the carotid bifurcation during acarotid endarterectomy procedure. In some cases the carotid bifurcationis closer to the level of the mandible, where access is more challengingand with less room available to separate it from the various nerveswhich should be spared. In these instances, the risk of inadvertentnerve injury can increase and an open endarterectomy procedure may notbe a good option.

Detailed Description of Retrograde Blood Flow System

As discussed, the retrograde flow system 100 includes the arterialaccess device 110, venous return device 115, and shunt 120 whichprovides a passageway for retrograde flow from the arterial accessdevice 110 to the venous return device 115. The system also includes theflow control assembly 125, which interacts with the shunt 120 toregulate and/or monitor retrograde blood flow through the shunt 120.Exemplary embodiments of the components of the retrograde flow system100 are now described.

Arterial Access Device

FIG. 6A shows an exemplary embodiment of the arterial access device 110,which comprises a distal sheath 605, a proximal extension 610, a flowline 615, an adaptor or Y-connector 620, and a hemostasis valve 625. Thedistal sheath 605 is adapted to be introduced through an incision orpuncture in a wall of a common carotid artery, either an open surgicalincision or a percutaneous puncture established, for example, using theSeldinger technique. The length of the sheath can be in the range from 5to 15 cm, usually being from 10 cm to 12 cm. The inner diameter istypically in the range from 7 Fr (1 Fr=0.33 mm), to 10 Fr, usually being8 Fr. Particularly when the sheath is being introduced through thetranscervical approach, above the clavicle but below the carotidbifurcation, it is desirable that the sheath 605 be highly flexiblewhile retaining hoop strength to resist kinking and buckling. Thus, thedistal sheath 605 can be circumferentially reinforced, such as by braid,helical ribbon, helical wire, or the like. In an alternate embodiment,the distal sheath is adapted to be introduced through a percutaneouspuncture into the femoral artery, such as in the groin, and up theaortic arch AA into the target common carotid artery CCA

The distal sheath 605 can have a stepped or other configuration having areduced diameter distal region 630, as shown in FIG. 6B, which shows anenlarged view of the distal region 630 of the sheath 605. The distalregion 630 of the sheath can be sized for insertion into the carotidartery, typically having an inner diameter in the range from 2.16 mm(0.085 inch) to 2.92 mm (0.115 inch) with the remaining proximal regionof the sheath having larger outside and luminal diameters, with theinner diameter typically being in the range from 2.794 mm (0.110 inch)to 3.43 mm (0.135 inch). The larger luminal diameter of the proximalregion minimizes the overall flow resistance of the sheath. In anembodiment, the reduced-diameter distal section 630 has a length ofapproximately 2 cm to 4 cm. The relatively short length of thereduced-diameter distal section 630 permits this section to bepositioned in the common carotid artery CCA via the transcervicalapproach with reduced risk that the distal end of the sheath 605 willcontact the bifurcation B. Moreover, the reduced diameter section 630also permits a reduction in size of the arteriotomy for introducing thesheath 605 into the artery while having a minimal impact in the level offlow resistance.

With reference again to FIG. 6A, the proximal extension 610 has an innerlumen which is contiguous with an inner lumen of the sheath 605. Thelumens can be joined by the Y-connector 620 which also connects a lumenof the flow line 615 to the sheath. In the assembled system, the flowline 615 connects to and forms a first leg of the retrograde shunt 120(FIG. 1). The proximal extension 610 can have a length sufficient tospace the hemostasis valve 625 well away from the Y-connector 620, whichis adjacent to the percutaneous or surgical insertion site. By spacingthe hemostasis valve 625 away from a percutaneous insertion site, thephysician can introduce a stent delivery system or other workingcatheter into the proximal extension 610 and sheath 605 while stayingout of the fluoroscopic field when fluoroscopy is being performed.

A flush line 635 can be connected to the side of the hemostasis valve625 and can have a stopcock 640 at its proximal or remote end. Theflush-line 635 allows for the introduction of saline, contrast fluid, orthe like, during the procedures. The flush line 635 can also allowpressure monitoring during the procedure. A dilator 645 having a tapereddistal end 650 can be provided to facilitate introduction of the distalsheath 605 into the common carotid artery. The dilator 645 can beintroduced through the hemostasis valve 625 so that the tapered distalend 650 extends through the distal end of the sheath 605, as best seenin FIG. 7A. The dilator 645 can have a central lumen to accommodate aguide wire. Typically, the guide wire is placed first into the vessel,and the dilator/sheath combination travels over the guide wire as it isbeing introduced into the vessel.

Optionally, a tube 705 may be provided which is coaxially received overthe exterior of the distal sheath 605, also as seen in FIG. 7A. The tube705 has a flared proximal end 710 which engages the adapter 620 and adistal end 715. Optionally, the distal end 715 may be beveled, as shownin FIG. 7B. The tube 705 may serve at least two purposes. First, thelength of the tube 705 limits the introduction of the sheath 605 to theexposed distal portion of the sheath 605, as seen in FIG. 7A. Second,the tube 705 can engage a pre-deployed puncture closure device disposedin the carotid artery wall, if present, to permit the sheath 605 to bewithdrawn without dislodging the closure device.

The distal sheath 605 can be configured to establish a curved transitionfrom a generally anterior-posterior approach over the common carotidartery to a generally axial luminal direction within the common carotidartery. The transition in direction is particularly useful when apercutaneous access is provided through the common carotid wall. Whilean open surgical access may allow for some distance in which to angle astraight sheath into the lumen of the common carotid artery,percutaneous access will generally be in a normal or perpendiculardirection relative to the access of the lumen, and in such cases, asheath that can flex or turn at an angle will find great use.

The sheath 605 can be formed in a variety of ways. For example, thesheath 605 can be pre-shaped to have a curve or an angle some setdistance from the tip, typically 2 to 3 cm. The pre-shaped curve orangle can typically provide for a turn in the range from 20° to 90°,preferably from 30° to 70°. For initial introduction, the sheath 605 canbe straightened with an obturator or other straight or shaped instrumentsuch as the dilator 645 placed into its lumen. After the sheath 605 hasbeen at least partially introduced through the percutaneous or otherarterial wall penetration, the obturator can be withdrawn to allow thesheath 605 to reassume its pre-shaped configuration into the arteriallumen.

Other sheath configurations include having a deflection mechanism suchthat the sheath can be placed and the catheter can be deflected in situto the desired deployment angle. In still other configurations, thecatheter has a non-rigid configuration when placed into the lumen of thecommon carotid artery. Once in place, a pull wire or other stiffeningmechanism can be deployed in order to shape and stiffen the sheath intoits desired configuration. One particular example of such a mechanism iscommonly known as “shape-lock” mechanisms as well described in medicaland patent literature.

Another sheath configuration comprises a curved dilator inserted into astraight but flexible sheath, so that the dilator and sheath are curvedduring insertion. The sheath is flexible enough to conform to theanatomy after dilator removal.

In an embodiment, the sheath has built-in puncturing capability andatraumatic tip analogous to a guide wire tip. This eliminates the needfor needle and wire exchange currently used for arterial accessaccording to the micropuncture technique, and can thus save time, reduceblood loss, and require less surgeon skill.

FIG. 8A shows another embodiment of the arterial access device 110. Thisembodiment is substantially the same as the embodiment shown in FIG. 6A,except that the distal sheath 605 includes an occlusion element 129 foroccluding flow through, for example the common carotid artery. If theoccluding element 129 is an inflatable structure such as a balloon orthe like, the sheath 605 can include an inflation lumen thatcommunicates with the occlusion element 129. The occlusion element 129can be an inflatable balloon, but it could also be an inflatable cuff, aconical or other circumferential element which flares outwardly toengage the interior wall of the common carotid artery to block flowtherepast, a membrane-covered braid, a slotted tube that radiallyenlarges when axially compressed, or similar structure which can bedeployed by mechanical means, or the like. In the case of balloonocclusion, the balloon can be compliant, non-compliant, elastomeric,reinforced, or have a variety of other characteristics. In anembodiment, the balloon is an elastomeric balloon which is closelyreceived over the exterior of the distal end of the sheath prior toinflation. When inflated, the elastomeric balloon can expand and conformto the inner wall of the common carotid artery. In an embodiment, theelastomeric balloon is able to expand to a diameter at least twice thatof the non-deployed configuration, frequently being able to be deployedto a diameter at least three times that of the undeployed configuration,more preferably being at least four times that of the undeployedconfiguration, or larger.

As shown in FIG. 8B, the distal sheath 605 with the occlusion element129 can have a stepped or other configuration having a reduced diameterdistal region 630. The distal region 630 can be sized for insertion intothe carotid artery with the remaining proximal region of the sheath 605having larger outside and luminal diameters, with the inner diametertypically being in the range from 2.794 mm (0.110 inch) to 3.43 mm(0.135 inch). The larger luminal diameter of the proximal regionminimizes the overall flow resistance of the sheath. In an embodiment,the reduced-diameter distal section 630 has a length of approximately 2cm to 4 cm. The relatively short length of the reduced-diameter distalsection 630 permits this section to be positioned in the common carotidartery CCA via the transcervical approach with reduced risk that thedistal end of the sheath 605 will contact the bifurcation B.

FIG. 2B shows an alternative embodiment, wherein the occlusion element129 can be introduced into the carotid artery on a second sheath 112separate from the distal sheath 605 of the arterial access device 110.The second or “proximal” sheath 112 can be adapted for insertion intothe common carotid artery in a proximal or “downward” direction awayfrom the cerebral vasculature. The second, proximal sheath can includean inflatable balloon 129 or other occlusion element, generally asdescribed above. The distal sheath 605 of the arterial access device 110can be then placed into the common carotid artery distal of the second,proximal sheath and generally oriented in a distal direction toward thecerebral vasculature. By using separate occlusion and access sheaths,the size of the arteriotomy needed for introducing the access sheath canbe reduced.

FIG. 2C shows yet another embodiment of a two arterial sheath system,wherein the interventional devices are introduced via an introducersheath 114 separate from the distal sheath 605 of the arterial device110. A second or “distal” sheath 114 can be adapted for insertion intothe common carotid artery distal to the arterial access device 110. Aswith the previous embodiment, the use of two separate access sheathsallows the size of each arteriotomy to be reduced.

Venous Return Device

Referring now to FIG. 9, the venous return device 115 can comprise adistal sheath 910 and a flow line 915, which connects to and forms a legof the shunt 120 when the system is in use. The distal sheath 910 isadapted to be introduced through an incision or puncture into a venousreturn location, such as the jugular vein or femoral vein. The distalsheath 910 and flow line 915 can be permanently affixed, or can beattached using a conventional luer fitting, as shown in FIG. 9.Optionally, as shown in FIG. 10, the sheath 910 can be joined to theflow line 915 by a Y-connector 1005. The Y-connector 1005 can include ahemostasis valve 1010, permitting insertion of a dilator 1015 tofacilitate introduction of the venous return device into the internaljugular vein or other vein. As with the arterial access dilator 645, thevenous dilator 1015 includes a central guide wire lumen so the venoussheath and dilator combination can be placed over a guide wire.Optionally, the venous sheath 910 can include a flush line 1020 with astopcock 1025 at its proximal or remote end.

In order to reduce the overall system flow resistance, the arterialaccess flow line 615 (FIG. 6A) and the venous return flow line 915, andY-connectors 620 (FIG. 6A) and 1005, can each have a relatively largeflow lumen inner diameter, typically being in the range from 2.54 mm(0.100 inch) to 5.08 mm (0.200 inch), and a relatively short length,typically being in the range from 10 cm to 20 cm. The low system flowresistance is desirable since it permits the flow to be maximized duringportions of a procedure when the risk of emboli is at its greatest. Thelow system flow resistance also allows the use of a variable flowresistance for controlling flow in the system, as described in moredetail below. The dimensions of the venous return sheath 910 can begenerally the same as those described for the arterial access sheath 605above. In the venous return sheath, an extension for the hemostasisvalve 1010 is not required.

Retrograde Shunt

The shunt 120 can be formed of a single tube or multiple, connectedtubes that provide fluid communication between the arterial accesscatheter 110 and the venous return catheter 115 to provide a pathway forretrograde blood flow therebetween. As shown in FIG. 1A, the shunt 120connects at one end (via connector 127 a) to the flow line 615 of thearterial access device 110, and at an opposite end (via connector 127 b)to the flow line 915 of the venous return catheter 115.

In an embodiment, the shunt 120 can be formed of at least one tube thatcommunicates with the flow control assembly 125. The shunt 120 can beany structure that provides a fluid pathway for blood flow. The shunt120 can have a single lumen or it can have multiple lumens. The shunt120 can be removably attached to the flow control assembly 125, arterialaccess device 110, and/or venous return device 115. Prior to use, theuser can select a shunt 120 with a length that is most appropriate foruse with the arterial access location and venous return location. In anembodiment, the shunt 120 can include one or more extension tubes thatcan be used to vary the length of the shunt 120. The extension tubes canbe modularly attached to the shunt 120 to achieve a desired length. Themodular aspect of the shunt 120 permits the user to lengthen the shunt120 as needed depending on the site of venous return. For example, insome patients, the internal jugular vein IJV is small and/or tortuous.The risk of complications at this site may be higher than at some otherlocations, due to proximity to other anatomic structures. In addition,hematoma in the neck may lead to airway obstruction and/or cerebralvascular complications. Consequently, for such patients it may bedesirable to locate the venous return site at a location other than theinternal jugular vein IJV, such as the femoral vein. A femoral veinreturn site may be accomplished percutaneously, with lower risk ofserious complication, and also offers an alternative venous access tothe central vein if the internal jugular vein UV is not available.Furthermore, the femoral venous return changes the layout of the reverseflow shunt such that the shunt controls may be located closer to the“working area” of the intervention, where the devices are beingintroduced and the contrast injection port is located.

In an embodiment, the shunt 120 has an internal diameter of 4.76 mm (3/16 inch) and has a length of 40-70 cm. As mentioned, the length of theshunt can be adjusted.

Flow Control Assembly—Regulation and Monitoring of Retrograde Flow

The flow control assembly 125 interacts with the retrograde shunt 120 toregulate and/or monitor the retrograde flow rate from the common carotidartery to the venous return site, such as the internal jugular vein, orto the external receptacle 130. In this regard, the flow controlassembly 125 enables the user to achieve higher maximum flow rates thanexisting systems and to also selectively adjust, set, or otherwisemodulate the retrograde flow rate. Various mechanisms can be used toregulate the retrograde flow rate, as described more fully below. Theflow control assembly 125 enables the user to configure retrograde bloodflow in a manner that is suited for various treatment regimens, asdescribed below.

In general, the ability to control the continuous retrograde flow rateallows the physician to adjust the protocol for individual patients andstages of the procedure. The retrograde blood flow rate will typicallybe controlled over a range from a low rate to a high rate. The high ratecan be at least two fold higher than the low rate, typically being atleast three fold higher than the low rate, and often being at least fivefold higher than the low rate, or even higher. In an embodiment, thehigh rate is at least three fold higher than the low rate and in anotherembodiment the high rate is at least six fold higher than the low rate.While it is generally desirable to have a high retrograde blood flowrate to maximize the extraction of emboli from the carotid arteries, theability of patients to tolerate retrograde blood flow will vary. Thus,by having a system and protocol which allows the retrograde blood flowrate to be easily modulated, the treating physician can determine whenthe flow rate exceeds the tolerable level for that patient and set thereverse flow rate accordingly. For patients who cannot toleratecontinuous high reverse flow rates, the physician can chose to turn onhigh flow only for brief, critical portions of the procedure when therisk of embolic debris is highest. At short intervals, for examplebetween 15 seconds and 1 minute, patient tolerance limitations areusually not a factor.

In specific embodiments, the continuous retrograde blood flow rate canbe controlled at a base line flow rate in the range from 10 ml/min to200 ml/min, typically from 20 ml/min to 100 ml/min. These flow rateswill be tolerable to the majority of patients. Although flow rate ismaintained at the base line flow rate during most of the procedure, attimes when the risk of emboli release is increased, the flow rate can beincreased above the base line for a short duration in order to improvethe ability to capture such emboli. For example, the retrograde bloodflow rate can be increased above the base line when the stent catheteris being introduced, when the stent is being deployed, pre- andpost-dilatation of the stent, removal of the common carotid arteryocclusion, and the like.

The flow rate control system can be cycled between a relatively low flowrate and a relatively high flow rate in order to “flush” the carotidarteries in the region of the carotid bifurcation prior toreestablishing antegrade flow. Such cycling can be established with ahigh flow rate which can be approximately two to six fold greater thanthe low flow rate, typically being about three fold greater. The cyclescan typically have a length in the range from 0.5 seconds to 10 seconds,usually from 2 seconds to 5 seconds, with the total duration of thecycling being in the range from 5 seconds to 60 seconds, usually from 10seconds to 30 seconds.

FIG. 11 shows an example of the system 100 with a schematicrepresentation of the flow control assembly 125, which is positionedalong the shunt 120 such that retrograde blood flow passes through orotherwise communicates with at least a portion of the flow controlassembly 125. The flow control assembly 125 can include variouscontrollable mechanisms for regulating and/or monitoring retrogradeflow. The mechanisms can include various means of controlling theretrograde flow, including one or more pumps 1110, valves 1115, syringes1120 and/or a variable resistance component 1125. The flow controlassembly 125 can be manually controlled by a user and/or automaticallycontrolled via a controller 1130 to vary the flow through the shunt 120.For example, varying the flow resistance, the rate of retrograde bloodflow through the shunt 120 can be controlled. The controller 1130, whichis described in more detail below, can be integrated into the flowcontrol assembly 125 or it can be a separate component that communicateswith the components of the flow control assembly 125.

In addition, the flow control assembly 125 can include one or more flowsensors 1135 and/or anatomical data sensors 1140 (described in detailbelow) for sensing one or more aspects of the retrograde flow. A filter1145 can be positioned along the shunt 120 for removing emboli beforethe blood is returned to the venous return site. When the filter 1145 ispositioned upstream of the controller 1130, the filter 1145 can preventemboli from entering the controller 1145 and potentially clogging thevariable flow resistance component 1125. It should be appreciated thatthe various components of the flow control assembly 125 (including thepump 1110, valves 1115, syringes 1120, variable resistance component1125, sensors 1135/1140, and filter 1145) can be positioned at variouslocations along the shunt 120 and at various upstream or downstreamlocations relative to one another. The components of the flow controlassembly 125 are not limited to the locations shown in FIG. 11.Moreover, the flow control assembly 125 does not necessarily include allof the components but can rather include various sub-combinations of thecomponents. For example, a syringe could optionally be used within theflow control assembly 125 for purposes of regulating flow or it could beused outside of the assembly for purposes other than flow regulation,such as to introduce fluid such as radiopaque contrast into the arteryin an antegrade direction via the shunt 120.

Both the variable resistance component 1125 and the pump 1110 can becoupled to the shunt 120 to control the retrograde flow rate. Thevariable resistance component 1125 controls the flow resistance, whilethe pump 1110 provides for positive displacement of the blood throughthe shunt 120. Thus, the pump can be activated to drive the retrogradeflow rather than relying on the perfusion stump pressures of the ECA andICA and the venous back pressure to drive the retrograde flow. The pump1110 can be a peristaltic tube pump or any type of pump including apositive displacement pump. The pump 1110 can be activated anddeactivated (either manually or automatically via the controller 1130)to selectively achieve blood displacement through the shunt 120 and tocontrol the flow rate through the shunt 120. Displacement of the bloodthrough the shunt 120 can also be achieved in other manners includingusing the aspiration syringe 1120, or a suction source such as avacutainer, vaculock syringe, or wall suction may be used. The pump 1110can communicate with the controller 1130.

One or more flow control valves 1115 can be positioned along the pathwayof the shunt. The valve(s) can be manually actuated or automaticallyactuated (via the controller 1130). The flow control valves 1115 can be,for example one-way valves to prevent flow in the antegrade direction inthe shunt 120, check valves, or high pressure valves which would closeoff the shunt 120, for example during high-pressure contrast injections(which are intended to enter the arterial vasculature in an antegradedirection).

The controller 1130 communicates with components of the system 100including the flow control assembly 125 to enable manual and/orautomatic regulation and/or monitoring of the retrograde flow throughthe components of the system 100 (including, for example, the shunt 120,the arterial access device 110, the venous return device 115 and theflow control assembly 125). For example, a user can actuate one or moreactuators on the controller 1130 to manually control the components ofthe flow control assembly 125. Manual controls can include switches ordials or similar components located directly on the controller 1130 orcomponents located remote from the controller 1130 such as a foot pedalor similar device. The controller 1130 can also automatically controlthe components of the system 100 without requiring input from the user.In an embodiment, the user can program software in the controller 1130to enable such automatic control. The controller 1130 can controlactuation of the mechanical portions of the flow control assembly 125.The controller 1130 can include circuitry or programming that interpretssignals generated by sensors 1135/1140 such that the controller 1130 cancontrol actuation of the flow control assembly 125 in response to suchsignals generated by the sensors.

The representation of the controller 1130 in FIG. 11 is merelyexemplary. It should be appreciated that the controller 1130 can vary inappearance and structure. The controller 1130 is shown in FIG. 11 asbeing integrated in a single housing. This permits the user to controlthe flow control assembly 125 from a single location. It should beappreciated that any of the components of the controller 1130 can beseparated into separate housings. Further, FIG. 11 shows the controller1130 and flow control assembly 125 as separate housings. It should beappreciated that the controller 1130 and flow control regulator 125 canbe integrated into a single housing or can be divided into multiplehousings or components.

Flow State Indicator(s)

The controller 1130 can include one or more indicators that provides avisual and/or audio signal to the user regarding the state of theretrograde flow. An audio indication advantageously reminds the user ofa flow state without requiring the user to visually check the flowcontroller 1130. The indicator(s) can include a speaker 1150 and/or alight 1155 or any other means for communicating the state of retrogradeflow to the user. The controller 1130 can communicate with one or moresensors of the system to control activation of the indicator. Or,activation of the indicator can be tied directly to the user actuatingone of the flow control actuators 1165. The indicator need not be aspeaker or a light. The indicator could simply be a button or switchthat visually indicates the state of the retrograde flow. For example,the button being in a certain state (such as a pressed or down state)may be a visual indication that the retrograde flow is in a high state.Or, a switch or dial pointing toward a particular labeled flow state maybe a visual indication that the retrograde flow is in the labeled state.

The indicator can provide a signal indicative of one or more states ofthe retrograde flow. In an embodiment, the indicator identifies only twodiscrete states: a state of “high” flow rate and a state of “low” flowrate. In another embodiment, the indicator identifies more than two flowrates, including a “high” flow rate, a “medium” flow rate, and a “low”rate. The indicator can be configured to identify any quantity ofdiscrete states of the retrograde flow or it can identify a graduatedsignal that corresponds to the state of the retrograde flow. In thisregard, the indicator can be a digital or analog meter 1160 thatindicates a value of the retrograde flow rate, such as in ml/min or anyother units.

In an embodiment, the indicator is configured to indicate to the userwhether the retrograde flow rate is in a state of “high” flow rate or a“low” flow rate. For example, the indicator may illuminate in a firstmanner (e.g., level of brightness) and/or emit a first audio signal whenthe flow rate is high and then change to a second manner of illuminationand/or emit a second audio signal when the flow rate is low. Or, theindicator may illuminate and/or emit an audio signal only when the flowrate is high, or only when the flow rate is low. Given that somepatients may be intolerant of a high flow rate or intolerant of a highflow rate beyond an extended period of time, it can be desirable thatthe indicator provide notification to the user when the flow rate is inthe high state. This would serve as a fail safe feature.

In another embodiment, the indicator provides a signal (audio and/orvisual) when the flow rate changes state, such as when the flow ratechanges from high to low and/or vice-versa. In another embodiment, theindicator provides a signal when no retrograde flow is present, such aswhen the shunt 120 is blocked or one of the stopcocks in the shunt 120is closed.

Flow Rate Actuators

The controller 1130 can include one or more actuators that the user canpress, switch, manipulate, or otherwise actuate to regulate theretrograde flow rate and/or to monitor the flow rate. For example, thecontroller 1130 can include a flow control actuator 1165 (such as one ormore buttons, knobs, dials, switches, etc.) that the user can actuate tocause the controller to selectively vary an aspect of the reverse flow.For example, in the illustrated embodiment, the flow control actuator1165 is a knob that can be turned to various discrete positions each ofwhich corresponds to the controller 1130 causing the system 100 toachieve a particular retrograde flow state. The states include, forexample, (a) OFF; (b) LO-FLOW; (c) HI-FLOW; and (d) ASPIRATE. It shouldbe appreciated that the foregoing states are merely exemplary and thatdifferent states or combinations of states can be used. The controller1130 achieves the various retrograde flow states by interacting with oneor more components of the system, including the sensor(s), valve(s),variable resistance component, and/or pump(s). It should be appreciatedthat the controller 1130 can also include circuitry and software thatregulates the retrograde flow rate and/or monitors the flow rate suchthat the user wouldn't need to actively actuate the controller 1130.

The OFF state corresponds to a state where there is no retrograde bloodflow through the shunt 120. When the user sets the flow control actuator1165 to OFF, the controller 1130 causes the retrograde flow to cease,such as by shutting off valves or closing a stop cock in the shunt 120.The LO-FLOW and HI-FLOW states correspond to a low retrograde flow rateand a high retrograde flow rate, respectively. When the user sets theflow control actuator 1165 to LO-FLOW or HI-FLOW, the controller 1130interacts with components of the flow control regulator 125 includingpump(s) 1110, valve(s) 1115 and/or variable resistance component 1125 toincrease or decrease the flow rate accordingly. Finally, the ASPIRATEstate corresponds to opening the circuit to a suction source, forexample a vacutainer or suction unit, if active retrograde flow isdesired.

The system can be used to vary the blood flow between various statesincluding an active state, a passive state, an aspiration state, and anoff state. The active state corresponds to the system using a means thatactively drives retrograde blood flow. Such active means can include,for example, a pump, syringe, vacuum source, etc. The passive statecorresponds to when retrograde blood flow is driven by the perfusionstump pressures of the ECA and ICA and possibly the venous pressure. Theaspiration state corresponds to the system using a suction source, forexample a vacutainer or suction unit, to drive retrograde blood flow.The off state corresponds to the system having zero retrograde bloodflow such as the result of closing a stopcock or valve. The low and highflow rates can be either passive or active flow states. In anembodiment, the particular value (such as in ml/min) of either the lowflow rate and/or the high flow rate can be predetermined and/orpre-programmed into the controller such that the user does not actuallyset or input the value. Rather, the user simply selects “high flow”and/or “low flow” (such as by pressing an actuator such as a button onthe controller 1130) and the controller 1130 interacts with one or moreof the components of the flow control assembly 125 to cause the flowrate to achieve the predetermined high or low flow rate value. Inanother embodiment, the user sets or inputs a value for low flow rateand/or high flow rate such as into the controller. In anotherembodiment, the low flow rate and/or high flow rate is not actually set.Rather, external data (such as data from the anatomical data sensor1140) is used as the basis for affects the flow rate.

The flow control actuator 1165 can be multiple actuators, for exampleone actuator, such as a button or switch, to switch state from LO-FLOWto HI-FLOW and another to close the flow loop to OFF, for example duringa contrast injection where the contrast is directed antegrade into thecarotid artery. In an embodiment, the flow control actuator 1165 caninclude multiple actuators. For example, one actuator can be operated toswitch flow rate from low to high, another actuator can be operated totemporarily stop flow, and a third actuator (such as a stopcock) can beoperated for aspiration using a syringe. In another example, oneactuator is operated to switch to LO-FLOW and another actuator isoperated to switch to HI-FLOW. Or, the flow control actuator 1165 caninclude multiple actuators to switch states from LO-FLOW to HI-FLOW andadditional actuators for fine-tuning flow rate within the high flowstate and low flow state. Upon switching between LO-FLOW and HI-FLOW,these additional actuators can be used to fine-tune the flow rateswithin those states. Thus, it should be appreciated that within eachstate (i.e. high flow state and low flow states) a variety of flow ratescan be dialed in and fine-tuned. A wide variety of actuators can be usedto achieve control over the state of flow.

The controller 1130 or individual components of the controller 1130 canbe located at various positions relative to the patient and/or relativeto the other components of the system 100. For example, the flow controlactuator 1165 can be located near the hemostasis valve where anyinterventional tools are introduced into the patient in order tofacilitate access to the flow control actuator 1165 during introductionof the tools. The location may vary, for example, based on whether atransfemoral or a transcervical approach is used, as shown in FIGS.1A-C. The controller 1130 can have a wireless connection to theremainder of the system 100 and/or a wired connection of adjustablelength to permit remote control of the system 100. The controller 1130can have a wireless connection with the flow control regulator 125and/or a wired connection of adjustable length to permit remote controlof the flow control regulator 125. The controller 1130 can also beintegrated in the flow control regulator 125. Where the controller 1130is mechanically connected to the components of the flow control assembly125, a tether with mechanical actuation capabilities can connect thecontroller 1130 to one or more of the components. In an embodiment, thecontroller 1130 can be positioned a sufficient distance from the system100 to permit positioning the controller 1130 outside of a radiationfield when fluoroscopy is in use.

The controller 1130 and any of its components can interact with othercomponents of the system (such as the pump(s), sensor(s), shunt, etc) invarious manners. For example, any of a variety of mechanical connectionscan be used to enable communication between the controller 1130 and thesystem components. Alternately, the controller 1130 can communicateelectronically or magnetically with the system components.Electro-mechanical connections can also be used. The controller 1130 canbe equipped with control software that enables the controller toimplement control functions with the system components. The controlleritself can be a mechanical, electrical or electro-mechanical device. Thecontroller can be mechanically, pneumatically, or hydraulically actuatedor electromechanically actuated (for example in the case of solenoidactuation of flow control state). The controller 1130 can include acomputer, computer processor, and memory, as well as data storagecapabilities.

Sensor(s)

As mentioned, the flow control assembly 125 can include or interact withone or more sensors, which communicate with the system 100 and/orcommunicate with the patient's anatomy. Each of the sensors can beadapted to respond to a physical stimulus (including, for example, heat,light, sound, pressure, magnetism, motion, etc.) and to transmit aresulting signal for measurement or display or for operating thecontroller 1130. In an embodiment, the flow sensor 1135 interacts withthe shunt 120 to sense an aspect of the flow through the shunt 120, suchas flow velocity or volumetric rate of blood flow. The flow sensor 1135could be directly coupled to a display that directly displays the valueof the volumetric flow rate or the flow velocity. Or the flow sensor1135 could feed data to the controller 1130 for display of thevolumetric flow rate or the flow velocity.

The type of flow sensor 1135 can vary. The flow sensor 1135 can be amechanical device, such as a paddle wheel, flapper valve, rolling ball,or any mechanical component that responds to the flow through the shunt120. Movement of the mechanical device in response to flow through theshunt 120 can serve as a visual indication of fluid flow and can also becalibrated to a scale as a visual indication of fluid flow rate. Themechanical device can be coupled to an electrical component. Forexample, a paddle wheel can be positioned in the shunt 120 such thatfluid flow causes the paddle wheel to rotate, with greater rate of fluidflow causing a greater speed of rotation of the paddle wheel. The paddlewheel can be coupled magnetically to a Hall-effect sensor to detect thespeed of rotation, which is indicative of the fluid flow rate throughthe shunt 120.

In an embodiment, the flow sensor 1135 is an ultrasonic orelectromagnetic flow meter, which allows for blood flow measurementwithout contacting the blood through the wall of the shunt 120. Anultrasonic or electromagnetic flow meter can be configured such that itdoes not have to contact the internal lumen of the shunt 120. In anembodiment, the flow sensor 1135 at least partially includes a Dopplerflow meter, such as a Transonic flow meter, that measures fluid flowthrough the shunt 120. It should be appreciated that any of a widevariety of sensor types can be used including an ultrasound flow meterand transducer. Moreover, the system can include multiple sensors.

The system 100 is not limited to using a flow sensor 1135 that ispositioned in the shunt 120 or a sensor that interacts with the venousreturn device 115 or the arterial access device 110. For example, ananatomical data sensor 1140 can communicate with or otherwise interactwith the patient's anatomy such as the patient's neurological anatomy.In this manner, the anatomical data sensor 1140 can sense a measurableanatomical aspect that is directly or indirectly related to the rate ofretrograde flow from the carotid artery. For example, the anatomicaldata sensor 1140 can measure blood flow conditions in the brain, forexample the flow velocity in the middle cerebral artery, and communicatesuch conditions to a display and/or to the controller 1130 foradjustment of the retrograde flow rate based on predetermined criteria.In an embodiment, the anatomical data sensor 1140 comprises atranscranial Doppler ultrasonography (TCD), which is an ultrasound testthat uses reflected sound waves to evaluate blood as it flows throughthe brain. Use of TCD results in a TCD signal that can be communicatedto the controller 1130 for controlling the retrograde flow rate toachieve or maintain a desired TCD profile. The anatomical data sensor1140 can be based on any physiological measurement, including reverseflow rate, blood flow through the middle cerebral artery, TCD signals ofembolic particles, or other neuromonitoring signals.

In an embodiment, the system 100 comprises a closed-loop control system.In the closed-loop control system, one or more of the sensors (such asthe flow sensor 1135 or the anatomical data sensor 1140) senses ormonitors a predetermined aspect of the system 100 or the anatomy (suchas, for example, reverse flow rate and/or neuromonitoring signal). Thesensor(s) feed relevant data to the controller 1130, which continuouslyadjusts an aspect of the system as necessary to maintain a desiredretrograde flow rate. The sensors communicate feedback on how the system100 is operating to the controller 1130 so that the controller 1130 cantranslate that data and actuate the components of the flow controlregulator 125 to dynamically compensate for disturbances to theretrograde flow rate. For example, the controller 1130 may includesoftware that causes the controller 1130 to signal the components of theflow control assembly 125 to adjust the flow rate such that the flowrate is maintained at a constant state despite differing blood pressuresfrom the patient. In this embodiment, the system 100 need not rely onthe user to determine when, how long, and/or what value to set thereverse flow rate in either a high or low state. Rather, software in thecontroller 1130 can govern such factors. In the closed loop system, thecontroller 1130 can control the components of the flow control assembly125 to establish the level or state of retrograde flow (either analoglevel or discreet state such as high, low, baseline, medium, etc.) basedon the retrograde flow rate sensed by the sensor 1135.

In an embodiment, the anatomical data sensor 1140 (which measures aphysiologic measurement in the patient) communicates a signal to thecontroller 1130, which adjusts the flow rate based on the signal. Forexample the physiological measurement may be based on flow velocitythrough the MCA, TCD signal, or some other cerebral vascular signal. Inthe case of the TCD signal, TCD may be used to monitor cerebral flowchanges and to detect microemboli. The controller 1130 may adjust theflow rate to maintain the TCD signal within a desired profile. Forexample, the TCD signal may indicate the presence of microemboli (“TCDhits”) and the controller 1130 can adjust the retrograde flow rate tomaintain the TCD hits below a threshold value of hits. (See, Ribo, etal., “Transcranial Doppler Monitoring of Transcervical Carotid Stentingwith Flow Reversal Protection: A Novel Carotid RevascularizationTechnique”, Stroke 2006, 37, 2846-2849; Shekel, et al., “Experience of500 Cases of Neurophysiological Monitoring in Carotid Endarterectomy”,Acta Neurochir, 2007, 149:681-689, which are incorporated by referencein their entirety.

In the case of the MCA flow, the controller 1130 can set the retrogradeflow rate at the “maximum” flow rate that is tolerated by the patient,as assessed by perfusion to the brain. The controller 1130 can thuscontrol the reverse flow rate to optimize the level of protection forthe patient without relying on the user to intercede. In anotherembodiment, the feedback is based on a state of the devices in thesystem 100 or the interventional tools being used. For example, a sensormay notify the controller 1130 when the system 100 is in a high riskstate, such as when an interventional catheter is positioned in thesheath 605. The controller 1130 then adjusts the flow rate to compensatefor such a state.

The controller 1130 can be used to selectively augment the retrogradeflow in a variety of manners. For example, it has been observed thatgreater reverse flow rates may cause a resultant greater drop in bloodflow to the brain, most importantly the ipsilateral MCA, which may notbe compensated enough with collateral flow from the Circle of Willis.Thus a higher reverse flow rate for an extended period of time may leadto conditions where the patient's brain is not getting enough bloodflow, leading to patient intolerance as exhibited by neurologicsymptoms. Studies show that MCA blood velocity less than 10 cm/sec is athreshold value below which patient is at risk for neurological blooddeficit. There are other markers for monitoring adequate perfusion tothe brains, such as EEG signals. However, a high flow rate may betolerated even up to a complete stoppage of MCA flow for a short period,up to about 15 seconds to 1 minute.

Thus, the controller 1130 can optimize embolic debris capture byautomatically increasing the reverse flow only during limited timeperiods which correspond to periods of heightened risk of emboligeneration during a procedure. These periods of heightened risk includethe period of time while an interventional device (such as a dilatationballoon for pre or post stenting dilatation or a stent delivery device)crosses the plaque P. Another period is during an interventionalmaneuver such as deployment of the stent or inflation and deflation ofthe balloon pre- or post-dilatation. A third period is during injectionof contrast for angiographic imaging of treatment area. During lowerrisk periods, the controller can cause the reverse flow rate to revertto a lower, baseline level. This lower level may correspond to a lowreverse flow rate in the ICA, or even slight antegrade flow in thosepatients with a high ECA to ICA perfusion pressure ratio.

In a flow regulation system where the user manually sets the state offlow, there is risk that the user may not pay attention to the state ofretrograde flow (high or low) and accidentally keep the circuit on highflow. This may then lead to adverse patient reactions. In an embodiment,as a safety mechanism, the default flow rate is the low flow rate. Thisserves as a fail safe measure for patient's that are intolerant of ahigh flow rate. In this regard, the controller 1130 can be biased towardthe default rate such that the controller causes the system to revert tothe low flow rate after passage of a predetermined period of time ofhigh flow rate. The bias toward low flow rate can be achieved viaelectronics or software, or it can be achieved using mechanicalcomponents, or a combination thereof. In an embodiment, the flow controlactuator 1165 of the controller 1130 and/or valve(s) 1115 and/or pump(s)1110 of the flow control regulator 125 are spring loaded toward a statethat achieves a low flow rate. The controller 1130 is configured suchthat the user may over-ride the controller 1130 such as to manuallycause the system to revert to a state of low flow rate if desired.

In another safety mechanism, the controller 1130 includes a timer 1170(FIG. 11) that keeps time with respect to how long the flow rate hasbeen at a high flow rate. The controller 1130 can be programmed toautomatically cause the system 100 to revert to a low flow rate after apredetermined time period of high flow rate, for example after 15, 30,or 60 seconds or more of high flow rate. After the controller reverts tothe low flow rate, the user can initiate another predetermined period ofhigh flow rate as desired. Moreover, the user can override thecontroller 1130 to cause the system 100 to move to the low flow rate (orhigh flow rate) as desired.

In an exemplary procedure, embolic debris capture is optimized while notcausing patient tolerance issues by initially setting the level ofretrograde flow at a low rate, and then switching to a high rate fordiscreet periods of time during critical stages in the procedure.Alternately, the flow rate is initially set at a high rate, and thenverifying patient tolerance to that level before proceeding with therest of the procedure. If the patient shows signs of intolerance, theretrograde flow rate is lowered. Patient tolerance may be determinedautomatically by the controller based on feedback from the anatomicaldata sensor 1140 or it may be determined by a user based on patientobservation. The adjustments to the retrograde flow rate may beperformed automatically by the controller or manually by the user.Alternately, the user may monitor the flow velocity through the middlecerebral artery (MCA), for example using TCD, and then to set themaximum level of reverse flow which keeps the MCA flow velocity abovethe threshold level. In this situation, the entire procedure may be donewithout modifying the state of flow. Adjustments may be made as neededif the MCA flow velocity changes during the course of the procedure, orthe patient exhibits neurologic symptoms.

Exemplary Mechanisms to Regulate Flow

The system 100 is adapted to regulate retrograde flow in a variety ofmanners. Any combination of the pump 1110, valve 1115, syringe 1120,and/or variable resistance component 1125 can be manually controlled bythe user or automatically controlled via the controller 1130 to adjustthe retrograde flow rate. Thus, the system 100 can regulate retrogradeflow in various manners, including controlling an active flow component(e.g., pump, syringe, etc.), reducing the flow restriction, switching toan aspiration source (such as a pre-set VacLock syringe, Vacutainer,suction system, or the like), or any combination thereof.

In the situation of FIG. 1D where an external receptacle or reservoir isused, the retrograde flow may be augmented in various manners. Thereservoir has a head height comprised of the height of the blood insidethe reservoir and the height of the reservoir with respect to thepatient. Reverse flow into the reservoir may be modulated by setting thereservoir height to increase or decrease the amount of pressure gradientfrom the CCA to the reservoir. In an embodiment, the reservoir is raisedto increase the reservoir pressure to a pressure that is greater thanvenous pressure. Or, the reservoir can be positioned below the patient,such as down to a level of the floor, to lower the reservoir pressure toa pressure below venous or atmospheric pressure.

The variable flow resistance in shunt 120 may be provided in a widevariety of ways. In this regard, flow resistance component 1125 cancause a change in the size or shape of the shunt to vary flow conditionsand thereby vary the flow rate. Or, the flow resistance component 1125can re-route the blood flow through one or more alternate flow pathwaysin the shunt to vary the flow conditions. Some exemplary embodiments ofthe flow resistance component 1125 are now described.

As shown in FIGS. 12A, 12B, 12C, and 12D, in an embodiment the shunt 120has an inflatable bladder 1205 formed along a portion of its interiorlumen. As shown in FIGS. 12A and 12C, when the bladder 1205 is deflated,the inner lumen of the shunt 120 remains substantially unrestricted,providing for a low resistance flow. By inflating the bladder 1205,however, as shown in FIGS. 12B and 12D, the flow lumen can be greatlyrestricted, thus greatly increasing the flow resistance and reducing theflow rate of atrial blood to the venous vasculature. The controller 1130can control inflation/deflation of the bladder 1205 or it can becontrolled manually by the user.

Rather than using an inflatable internal bladder, as shown in FIGS.12A-12D, the cross-sectional area of the lumen in the shunt 120 may bedecreased by applying an external force, such as flattening the shunt120 with a pair of opposed plates 1405, as shown in FIGS. 13A-13D. Theopposed plates are adapted to move toward and away from one another withthe shunt 120 positioned between the plates. When the plates 1405 arespaced apart, as shown in FIGS. 13A and 13C, the lumen of the shunt 120remains unrestricted. When the plates 1405 are closed on the shunt 120,as shown in FIGS. 13B and 13D, in contrast, the plates 1405 constrictthe shunt 120. In this manner, the lumen remaining in shunt 120 can begreatly decreased to increase flow resistance through the shunt. Thecontroller 1130 can control movement of the plates 1405 or such movementcan be controlled manually by the user.

Referring now to FIGS. 14A and 14B, the available cross-sectional areaof the shunt 120 can also be restricted by axially elongating a portion1505 of the shunt 120. Prior to axial elongation, the portion 1505 willbe generally unchanged, providing a full luminal flow area in theportion 1505, as shown in FIG. 14A. By elongating the portion 1505,however, as shown in FIG. 14B, the internal luminal area of the shunt120 in the portion 1505 can be significantly decreased and the lengthincreased, both of which have the effect of increasing the flowresistance. When employing axial elongation to reduce the luminal areaof shunt 120, it will be advantageous to employ a mesh or braidstructure in the shunt at least in the portion 1505. The mesh or braidstructure provides the shunt 120 with a pliable feature that facilitatesaxial elongation without breaking. The controller 1130 can controlelongation of the shunt 120 or such it can be controlled manually by theuser.

Referring now to FIGS. 15A-15D, instead of applying an external force toreduce the cross-sectional area of shunt 120, a portion of the shunt 120can be made with a small diameter to begin with, as shown in FIGS. 15Aand 15C. The shunt 120 passes through a chamber 1600 which is sealed atboth ends. A vacuum is applied within the chamber 1600 exterior of theshunt 120 to cause a pressure gradient. The pressure gradient cause theshunt 120 to increase in size within the chamber 120, as shown in FIGS.12B and 12D. The vacuum may be applied in a receptacle 1605 attached toa vacuum source 1610. Conversely, a similar system may be employed witha shunt 120 whose resting configuration is in the increased size.Pressure may be applied to the chamber to shrink or flatten the shunt todecrease the flow resistance. The controller 1130 can control the vacuumor it can be controlled manually by the user.

As yet another alternative, the flow resistance through shunt 120 may bechanged by providing two or more alternative flow paths. As shown inFIG. 16A, the flow through shunt 120 passes through a main lumen 1700 aswell as secondary lumen 1705. The secondary lumen 1705 is longer and/orhas a smaller diameter than the main lumen 1700. Thus, the secondarylumen 1705 has higher flow resistance than the main lumen 1700. Bypassing the blood through both these lumens, the flow resistance will beat a minimum. Blood is able to flow through both lumens 1700 and 1705due to the pressure drop created in the main lumen 1700 across the inletand outlet of the secondary lumen 1705. This has the benefit ofpreventing stagnant blood. As shown in FIG. 16B, by blocking flowthrough the main lumen 1700 of shunt 120, the flow can be divertedentirely to the secondary lumen 1705, thus increasing the flowresistance and reducing the blood flow rate. It will be appreciated thatadditional flow lumens could also be provided in parallel to allow for athree, four, or more discrete flow resistances. The shunt 120 may beequipped with a valve 1710 that controls flow to the main lumen 1700 andthe secondary lumen 1705 with the valve 1710 being controlled by thecontroller 1130 or being controlled manually by the user. The embodimentof FIGS. 16A and 16B has an advantage in that this embodiment in that itdoes not require as small of lumen sizes to achieve desired retrogradeflow rates as some of the other embodiments of variable flow resistancemechanisms. This is a benefit in blood flow lines in that there is lesschance of clogging and causing clots in larger lumen sizes than smallerlumen sizes.

The shunt 120 can also be arranged in a variety of coiled configurationswhich permit external compression to vary the flow resistance in avariety of ways. Arrangement of a portion of the shunt 120 in a coilcontains a long section of the shunt in a relatively small area. Thisallows compression of a long length of the shunt 120 over a small space.As shown in FIGS. 17A and 17B, a portion of the shunt 120 is woundaround a dowel 1805 to form a coiled region. The dowel 1805 has plates1810 a and 1810 b which can move toward and away from each other in anaxial direction. When plates 1810 a and 1810 b are moved away from eachother, the coiled portion of the shunt 105 is uncompressed and flowresistance is at a minimum. The shunt 120 is large diameter, so when theshunt is non-compressed, the flow resistance is low, allowing ahigh-flow state. To down-regulate the flow, the two plates 1810 a and1810 b are pushed together, compressing the coil of shunt 120. By movingthe plates 1810 a and 1810 b together, as shown in FIG. 17B, the coiledportion of the shunt 120 is compressed to increase the flow resistance.The controller 1130 can control the plates or they can be controlledmanually by the user.

A similar compression apparatus is shown in FIGS. 18A and 18B. In thisconfiguration, the coiled shunt 120 is encased between two movablecylinder halves 1905 a and 1905 b. The halves 1905 a and 1905 b canslide along dowel pins 1910 to move toward and away from one another.When the cylinder halves 1905 are moved apart, the coiled shunt 120 isuncompressed and flow resistance is at a minimum. When the cylinderhalves 1905 are brought together, the coiled shunt 120 is compressedcircumferentially to increase flow resistance. The controller 1130 cancontrol the halves 1905 or they can be controlled manually by the user.

As shown in FIGS. 19A through 19D, the shunt 120 may also be woundaround an axially split mandrel 2010 having wedge elements 2015 onopposed ends. By axially translating wedge elements 2015 in and out ofthe split mandrel 2010, the split portions of the mandrel are opened andclosed relative to one another, causing the coil of tubing to bestretched (when the mandrel portions 2010 are spread apart, FIG. 19C,19D) or relaxed (when the mandrel portions 2010 are closed, FIG. 19A,19B.) Thus, when the wedge elements 2015 are spaced apart, as shown inFIGS. 19A and 19B, the outward pressure on the shunt 120 is at a minimumand the flow resistance is also at a minimum. By driving the wedgeelements 2015 inwardly, as shown in FIGS. 19C and 19D, the split mandrelhalves 2020 are forced apart and the coil of shunt 120 is stretched.This has the dual effect of decreasing the cross sectional area of theshunt and lengthening the shunt in the coiled region, both of which leadto increased flow resistance.

FIGS. 20A and 20B show an embodiment of the variable resistancecomponent 1125 that uses a dowel to vary the resistance to flow. Ahousing 2030 is inserted into a section of the shunt 120. The housing2030 has an internal lumen 2035 that is contiguous with the internallumen of the shunt 120. A dowel 2040 can move into and out of a portionof the internal lumen 2035. As shown in FIG. 20A, when the dowel 2040 isinserted into the internal lumen 2035, the internal lumen 2035 isannular with a cross-sectional area that is much smaller than thecross-sectional area of the internal lumen 2035 when the dowel is notpresent. Thus, flow resistance increases when the dowel 2040 ispositioned in the internal lumen 2035. The annular internal lumen 2035has a length S that can be varied by varying the portion of the dowel2040 that is inserted into the lumen 2035. Thus, as more of the dowel2040 is inserted, the length S of the annular lumen 2035 increases andvice-versa. This can be used to vary the level of flow resistance causedby the presence of the dowel 2040.

The dowel 2040 enters the internal lumen 2035 via a hemostasis valve inthe housing 2030. A cap 2050 and an O-ring 2055 provide a sealingengagement that seals the housing 2030 and dowel 2040 against leakage.The cap 2050 may have a locking feature, such as threads, that can beused to lock the cap 2050 against the housing 2030 and to also fix theposition of the dowel 2040 in the housing 2040. When the cap 2050 islocked or tightened, the cap 2050 exerts pressure against the O-ring2055 to tighten it against the dowel 2040 in a sealed engagement. Whenthe cap 2050 is unlocked or untightened, the dowel 2040 is free to movein and out of the housing 2030.

Exemplary Methods of Use

Referring now to FIGS. 21A-21E, flow through the carotid arterybifurcation at different stages of the methods of the present disclosurewill be described. Initially, as shown in FIG. 21A, the distal sheath605 of the arterial access device 110 is introduced into the commoncarotid artery CCA. As mentioned, entry into the common carotid arteryCCA can be via a transcervical or transfemoral approach. After thesheath 605 of the arterial access device 110 has been introduced intothe common carotid artery CCA, the blood flow will continue in antegradedirection AG with flow from the common carotid artery entering both theinternal carotid artery ICA and the external carotid artery ECA, asshown in FIG. 21A.

The venous return device 115 is then inserted into a venous return site,such as the internal jugular vein IJV (not shown in FIGS. 21A-21E). Theshunt 120 is used to connect the flow lines 615 and 915 of the arterialaccess device 110 and the venous return device 115, respectively (asshown in FIG. 1A). In this manner, the shunt 120 provides a passagewayfor retrograde flow from the atrial access device 110 to the venousreturn device 115. In another embodiment, the shunt 120 connects to anexternal receptacle 130 rather than to the venous return device 115, asshown in FIG. 1C.

Once all components of the system are in place and connected, flowthrough the common carotid artery. CCA is stopped, typically using theocclusion element 129 as shown in FIG. 21B. The occlusion element 129 isexpanded at a location proximal to the distal opening of the sheath 605to occlude the CCA. Alternately, the tourniquet 2105 (FIG. 1A) or otherexternal vessel occlusion device can be used to occlude the commoncarotid artery CCA to stop flow therethrough. In an alternativeembodiment, the occlusion element 129 is introduced on second occlusiondevice 112 separate from the distal sheath 605 of the arterial accessdevice 110, as shown in FIG. 2B. The ECA may also be occluded with aseparate occlusion element, either on the same device 110 or on aseparate occlusion device.

At that point retrograde flow RG from the external carotid artery ECAand internal carotid artery ICA will begin and will flow through thesheath 605, the flow line 615, the shunt 120, and into the venous returndevice 115 via the flow line 915. The flow control assembly 125regulates the retrograde flow as described above. FIG. 21B shows theoccurrence of retrograde flow RG. While the retrograde flow ismaintained, a stent delivery catheter 2110 is introduced into the sheath605, as shown in FIG. 21C. The stent delivery catheter 2110 isintroduced into the sheath 605 through the hemostasis valve 615 and theproximal extension 610 (not shown in FIGS. 21A-21E) of the arterialaccess device 110. The stent delivery catheter 2110 is advanced into theinternal carotid artery ICA and a stent 2115 deployed at the bifurcationB, as shown in FIG. 21D.

The rate of retrograde flow can be increased during periods of higherrisk for emboli generation for example while the stent delivery catheter2110 is being introduced and optionally while the stent 2115 is beingdeployed. The rate of retrograde flow can be increased also duringplacement and expansion of balloons for dilatation prior to or afterstent deployment. An atherectomy can also be performed before stentingunder retrograde flow.

Still further optionally, after the stent 2115 has been expanded, thebifurcation B can be flushed by cycling the retrograde flow between alow flow rate and high flow rate. The region within the carotid arterieswhere the stent has been deployed or other procedure performed may beflushed with blood prior to reestablishing normal blood flow. Inparticular, while the common carotid artery remains occluded, a ballooncatheter or other occlusion element may be advanced into the internalcarotid artery and deployed to fully occlude that artery. The samemaneuver may also be used to perform a post-deployment stent dilatation,which is typically done currently in self-expanding stent procedures.Flow from the common carotid artery and into the external carotid arterymay then be reestablished by temporarily opening the occluding meanspresent in the artery. The resulting flow will thus be able to flush thecommon carotid artery which saw slow, turbulent, or stagnant flow duringcarotid artery occlusion into the external carotid artery. In addition,the same balloon may be positioned distally of the stent during reverseflow and forward flow then established by temporarily relievingocclusion of the common carotid artery and flushing. Thus, the flushingaction occurs in the stented area to help remove loose or looselyadhering embolic debris in that region.

Optionally, while flow from the common carotid artery continues and theinternal carotid artery remains blocked, measures can be taken tofurther loosen emboli from the treated region. For example, mechanicalelements may be used to clean or remove loose or loosely attached plaqueor other potentially embolic debris within the stent, thrombolytic orother fluid delivery catheters may be used to clean the area, or otherprocedures may be performed. For example, treatment of in-stentrestenosis using balloons, atherectomy, or more stents can be performedunder retrograde flow In another example, the occlusion balloon cathetermay include flow or aspiration lumens or channels which open proximal tothe balloon. Saline, thrombolytics, or other fluids may be infusedand/or blood and debris aspirated to or from the treated area withoutthe need for an additional device. While the emboli thus released willflow into the external carotid artery, the external carotid artery isgenerally less sensitive to emboli release than the internal carotidartery. By prophylactically removing potential emboli which remain, whenflow to the internal carotid artery is reestablished, the risk of embolirelease is even further reduced. The emboli can also be released underretrograde flow so that the emboli flows through the shunt 120 to thevenous system, a filter in the shunt 120, or the receptacle 130.

After the bifurcation has been cleared of emboli, the occlusion element129 or alternately the tourniquet 2105 can be released, reestablishingantegrade flow, as shown in FIG. 21E. The sheath 605 can then beremoved.

A self-closing element may be deployed about the penetration in the wallof the common carotid artery prior to withdrawing the sheath 605 at theend of the procedure. Usually, the self-closing element will be deployedat or near the beginning of the procedure, but optionally, theself-closing element could be deployed as the sheath is being withdrawn,often being released from a distal end of the sheath onto the wall ofthe common carotid artery. Use of the self-closing element isadvantageous since it affects substantially the rapid closure of thepenetration in the common carotid artery as the sheath is beingwithdrawn. Such rapid closure can reduce or eliminate unintended bloodloss either at the end of the procedure or during accidentaldislodgement of the sheath. In addition, such a self-closing element mayreduce the risk of arterial wall dissection during access. Further, theself-closing element may be configured to exert a frictional or otherretention force on the sheath during the procedure. Such a retentionforce is advantageous and can reduce the chance of accidentallydislodging the sheath during the procedure. A self-closing elementeliminates the need for vascular surgical closure of the artery withsuture after sheath removal, reducing the need for a large surgicalfield and greatly reducing the surgical skill required for theprocedure.

The disclosed systems and methods may employ a wide variety ofself-closing elements, typically being mechanical elements which includean anchor portion and a self-closing portion. The anchor portion maycomprise hooks, pins, staples, dips, tine, suture, or the like, whichare engaged in the exterior surface of the common carotid artery aboutthe penetration to immobilize the self-closing element when thepenetration is fully open. The self-closing element may also include aspring-like or other self-closing portion which, upon removal of thesheath, will close the anchor portion in order to draw the tissue in thearterial wall together to provide closure. Usually, the closure will besufficient so that no further measures need be taken to close or sealthe penetration. Optionally, however, it may be desirable to provide forsupplemental sealing of the self-closing element after the sheath iswithdrawn. For example, the self-closing element and/or the tissue tractin the region of the element can be treated with hemostatic materials,such as bioabsorbable polymers, collagen plugs, glues, sealants,clotting factors, or other clot-promoting agents. Alternatively, thetissue or self-closing element could be sealed using other sealingprotocols, such as electrocautery, suturing, clipping, stapling, or thelike. In another method, the self-closing element will be a self-sealingmembrane or gasket material which is attached to the outer wall of thevessel with clips, glue, bands, or other means. The self-sealingmembrane may have an inner opening such as a slit or cross cut, whichwould be normally closed against blood pressure. Any of theseself-closing elements could be designed to be placed in an open surgicalprocedure, or deployed percutaneously.

In another embodiment, carotid artery stenting may be performed afterthe sheath is placed and an occlusion balloon catheter deployed in theexternal carotid artery. The stent having a side hole or other elementintended to not block the ostium of the external carotid artery may bedelivered through the sheath with a guidewire or a shaft of an externalcarotid artery occlusion balloon received through the side hole. Thus,as the stent is advanced, typically by a catheter being introduced overa guidewire which extends into the internal carotid artery, the presenceof the catheter shaft in the side hole will ensure that the side holebecomes aligned with the ostium to the external carotid artery as thestent is being advanced. When an occlusion balloon is deployed in theexternal carotid artery, the side hole prevents trapping the externalcarotid artery occlusion balloon shaft with the stent which is adisadvantage of the other flow reversal systems. This approach alsoavoids “jailing” the external carotid artery, and if the stent iscovered with a graft material, avoids blocking flow to the externalcarotid artery.

In another embodiment, stents are placed which have a shape whichsubstantially conforms to any preexisting angle between the commoncarotid artery and the internal carotid artery. Due to significantvariation in the anatomy among patients, the bifurcation between theinternal carotid artery and the external carotid artery may have a widevariety of angles and shapes. By providing a family of stents havingdiffering geometries, or by providing individual stents which may beshaped by the physician prior to deployment, the physician may choose astent which matches the patient's particular anatomy prior todeployment. The patient's anatomy may be determined using angiography orby other conventional means. As a still further alternative, the stentmay have sections of articulation. These stents may be placed first andthen articulated in situ in order to match the angle of bifurcationbetween a common carotid artery and internal carotid artery. Stents maybe placed in the carotid arteries, where the stents have a sidewall withdifferent density zones.

In another embodiment, a stent may be placed where the stent is at leastpartly covered with a graft material at either or both ends. Generally,the stent will be free from graft material and the middle section of thestent which will be deployed adjacent to the ostium to the externalcarotid artery to allow blood flow from the common carotid artery intothe external carotid artery.

In another embodiment, a stent delivery system can be optimized fortranscervical access by making them shorter and more rigid than systemsdesigned for transfemoral access. These changes will improve the abilityto torque and position the stent accurately during deployment. Inaddition, the stent delivery system can be designed to align the stentwith the ostium of the external carotid artery, either by using theexternal carotid occlusion balloon or a separate guide wire in theexternal carotid artery, which is especially useful with stents withsideholes or for stents with curves, bends, or angulation whereorientation is critical.

In certain embodiments, the shunt is fixedly connected to the arterialaccess sheath and the venous return sheath so that the entire assemblyof the replaceable flow assembly and sheaths may be disposable andreplaceable as a unit. In other instances, the flow control assembly maybe removably attached to either or both of the sheaths.

In an embodiment, the user first determines whether any periods ofheightened risk of emboli generation may exist during the procedure. Asmentioned, some exemplary periods of heightened risk include (1) duringperiods when the plaque P is being crossed by a device; (2) during aninterventional procedure, such as during delivery of a stent or duringinflation or deflation of a balloon catheter or guidewire; (3) duringinjection or contrast. The foregoing are merely examples of periods ofheightened risk. During such periods, the user sets the retrograde flowat a high rate for a discreet period of time. At the end of the highrisk period, or if the patient exhibits any intolerance to the high flowrate, then the user reverts the flow state to baseline flow. If thesystem has a timer, the flow state automatically reverts to baselineflow after a set period of time. In this case, the user may re-set theflow state to high flow if the procedure is still in a period ofheightened embolic risk.

In another embodiment, if the patient exhibits an intolerance to thepresence of retrograde flow, then retrograde flow is established onlyduring placement of a filter in the ICA distal to the plaque P.Retrograde flow is then ceased while an interventional procedure isperformed on the plaque P. Retrograde flow is then re-established whilethe filter is removed. In another embodiment, a filter is places in theICA distal of the plaque P and retrograde flow is established while thefilter is in place. This embodiment combines the use of a distal filterwith retrograde flow.

Although embodiments of various methods and devices are described hereinin detail with reference to certain versions, it should be appreciatedthat other versions, embodiments, methods of use, and combinationsthereof are also possible. Therefore the spirit and scope of theappended claims should not be limited to the description of theembodiments contained herein.

1. A system for use in accessing and treating a carotid, said systemcomprising: an arterial access device adapted to be introduced into acommon carotid artery and receive blood flow from the carotid artery; ashunt fluidly connected to the arterial access device, wherein the shuntprovides a pathway for blood to flow from the arterial access device toa return site; a flow control assembly coupled to the shunt and adaptedto regulate blood flow through the shunt between at least a first bloodflow state and at least a second blood flow state, wherein the flowcontrol assembly includes one or more components that interact with theblood flow through the shunt; and a one-way valve coupled to the shunt,wherein the valve prevents fluid flow through the shunt in a directiontowards the arterial access device.
 2. A system as in claim 1, furthercomprising a port fluidly communicating with the shunt, wherein the portmay be used to connect an aspiration device to the shunt.
 3. A system asin claim 2, further comprising a valve which controls fluidcommunication between the shunt and the port.
 4. A system as in claim 3,wherein the valve automatically opens with attachment of an aspirationor injection device, and wherein the valve automatically closes withremoval of the aspiration or injection device.
 5. A system as in claim2, wherein the aspiration device is a syringe, a vacuum-lock syringe, avacuum syringe, a suction pump, or other aspiration source.
 6. A systemas in claim 1, further comprising: a fluid line communicating with theshunt, and wherein the fluid line may be used to connect an injection oraspiration device to the shunt line.
 7. A system as in claim 6, whereina connection of the fluid line to the shunt is contained within ahousing of the flow control assembly
 8. A system as in claim 6, whereina connection of the fluid line to the shunt is outside a housing of theflow control assembly.
 9. A system as in claim 6, wherein flow controlassembly contains an actuator adapted to open communication between thefluid line and the shunt.
 10. A system as in claim 9, wherein theactuator can be manually actuated by a user to both open and close aconnection between the fluid line and the shunt.
 11. A system as inclaim 9, wherein the actuator closes the shunt line towards the returnsite when the actuator opens the connection between the fluid line andthe shunt.
 12. A system as in claim 9, wherein the actuatorautomatically reverts to close the fluid line connection and open theshunt connection to the return site when the aspiration is complete. 13.A system as in claim 1, wherein the shunt further comprises an activepump comprising active pump controls.
 14. A system as in claim 13,wherein the active pump controls are coupled to a housing of the flowcontrol assembly.
 15. A system as in claim 13, wherein the active pumpcontrols are separate from a housing of the flow control assembly.
 16. Asystem as in claim 13, wherein the active pump fluid pathway is inparallel to a passive flow control fluid pathway.
 17. A system as inclaim 13, wherein the flow control assembly comprises two or moreparallel flow paths of the shunt, and a valve to open or close one ormore of the flow paths to adjust the state of flow by selectively directblood flow through one or more of the flow paths, and wherein the activepump is attached to one of the parallel flow paths.
 18. A system as inclaim 13, wherein the active pump fluid path is coupled in series to thepassive flow control fluid pathway.
 19. A system as in claim 18, whereinthe active pump allows passive flow when the active pump is inactive.20. A system as in claim 13, wherein the active pump is a roller pump, apositive displacement pump, a syringe pump, or an impeller pump.
 21. Amethod for accessing and treating a carotid, comprising: forming apenetration in a wall of a common carotid artery; positioning anarterial access sheath through the penetration; connecting a flow shuntfrom the arterial access sheath to a return site, wherein the flow shuntis coupled to a one way valve that permits fluid flow through the shuntin a direction towards a return site; blocking antegrade blood flow fromthe common carotid artery past the sheath; allowing retrograde bloodflow from the internal carotid artery via the sheath and the shunt tothe return site while the common carotid artery remains blocked; andadjusting the state of retrograde blood flow through the sheath andshunt.
 22. A method as in claim 21, further comprising attaching anaspiration device to the flow shunt and aspirating fluid from the shunt.23. A method as in claim 22, wherein the aspiration device comprises adiscreet vacuum source, and wherein aspirating from the shunt comprisesopening a valve between the shunt and the vacuum source.
 24. A devicefor use in accessing and treating a carotid or cerebral artery, saiddevice comprising: a sheath having a distal portion, a proximal portion,and a lumen extending between the distal and proximal portion, whereinthe sheath is stepped or tapered such that the diameter of the sheath atthe proximal portion is greater than the diameter of the sheath at thedistal portion; a hemostasis valve at a proximal region of the sheath,the hemostasis valve being adapted to inhibit blood flow from the sheathwhile allowing device introduction into the sheath; and an inflatableocclusion member at the distal region of the sheath.
 25. A device as inclaim 24, wherein the distal portion is adapted to be inserted into thecommon carotid artery, and wherein the inflatable occlusion member isadapted to occlude the common carotid artery.
 26. A device as in claim25, wherein the distal portion has an inner diameter in the range fromabout 0.110 inch to 0.135 inch.
 27. A device as in claim 25, wherein thedistal portion has a length from about 2 to 4 cm.
 28. A device as inclaim 24, further comprising a flow line having a lumen fluidlyconnected to the sheath, the flow line connected near the proximal endof the sheath so that blood can flow from the sheath into the flow line.29. A system for use in accessing and treating a carotid, said systemcomprising: an arterial access device adapted to be introduced into acommon carotid artery and receive blood flow from the carotid artery,wherein the arterial access device comprises a sheath having a steppedor tapered diameter such that the diameter at the proximal end of thesheath is greater than the diameter at the distal end of the sheath; ashunt fluidly connected to the arterial access device, wherein the shuntprovides a pathway for blood to flow from the arterial access device toa return site; and a flow control assembly coupled to the shunt andadapted to regulate blood flow through the shunt between at least afirst blood flow state and at least a second blood flow state, whereinthe flow control assembly includes one or more components that interactwith the blood flow through the shunt.
 30. A system as in claim 29,further comprising an inflatable occlusion member on a distal region ofthe sheath.
 31. A system as in claim 29, wherein the distal end of thesheath is adapted to be inserted into the common carotid artery, andwherein the inflatable occlusion member is adapted to occlude the commoncarotid artery.
 32. A system as in claim 29, wherein the distal end ofthe sheath is adapted to be inserted into the internal carotid arteryand the proximal end is adapted to be inserted into the common carotidartery, and wherein the occlusion member is adapted to occlude theinternal carotid artery.
 33. A method for accessing and treating acarotid artery, comprising: forming a penetration in a wall of a commoncarotid artery; positioning an arterial access sheath having a distalend and an inflatable occlusion member through the penetration, whereinthe distal end of the sheath is adapted to be inserted into the commoncarotid artery, and wherein the inflatable occlusion member is adaptedto occlude the common carotid artery; placing a distal embolicprotection device through the arterial access sheath into the internalcarotid artery distal to a treatment site; and performing a procedure onthe carotid artery.
 34. A method as in claim 33, wherein the distalembolic protection device is a distal filter.
 35. A method for accessingand treating a carotid artery, comprising: forming a penetration in awall of a common carotid artery; positioning an arterial access sheaththrough the penetration; blocking blood flow from the common carotidartery past the sheath; allowing retrograde blood flow from the carotidartery into the sheath through a flow path; placing a distal embolicprotection device through the arterial access sheath into the internalcarotid artery distal to a treatment site; unblocking blood flow fromthe common carotid artery past the sheath and closing the flow path torestore antegrade flow to the internal carotid artery; and performing aprocedure on the carotid artery.
 36. The method as in claim 35, furthercomprising the steps of: re-blocking the blood flow from the commoncarotid artery and reestablishing retrograde blood flow in the internalcarotid artery; and removing the distal embolic protection device. 37.The method as in claim 35, wherein performing a procedure comprisesplacing a stent.
 38. A method for accessing and treating a carotidartery, comprising: forming a penetration in a wall of a common carotidartery; positioning an arterial access sheath through the penetration;blocking blood flow from the common carotid artery past the sheath;aspirating from the arterial access sheath to create retrograde bloodflow from the carotid artery while the common carotid artery remainsblocked; placing a distal embolic protection device during theaspiration step through the arterial access sheath into the internalcarotid artery distal to a treatment site; unblocking blood flow fromthe common carotid artery past the sheath to restore antegrade flow tothe internal carotid artery; and performing a procedure on the carotidartery.
 39. The method as in claim 38, further comprising the steps of:re-blocking blood flow from the common carotid artery past the sheath;aspirating from the arterial access sheath while removing the distalembolic protection device.
 40. The method as in claim 38, whereinperforming a procedure comprises placing a stent.